A method to obtain a metal oxide semiconductor via decomposition oxidation (heat decomposition reaction) of a metal salt or an organic metal has been known.
As a technology to carry out decomposition oxidation (heat decomposition reaction) on an organic metal to obtain an oxide semiconductor, for example, the methods disclosed in Patent Documents 1 and 2 are known.
In these methods, thermal oxidation or plasma oxidation is usually used for the oxidation of a precursor. However, when a thermal oxidation method is used to oxidize a precursor, a very high temperature range of at least 400° C. or more, substantially, 550° C. or more is usually needed to obtain a desired property. Accordingly, the energy efficiency is not high, a relatively long processing time is needed, and the application of a light and flexible resin substrate becomes difficult because the temperature of the substrate increases as high as the treatment temperature while being treated.
In the case of plasma oxidation, since the treatment is carried out in an extremely reactive plasma space, there has been a problem that the electrode or the insulating layer is degraded in the thin film transistor manufacturing process, whereby the mobility and the off electric current (dark current) turns worse.
Also, a method to obtain a metal oxide semiconductor via such as a thermal oxidation using an organic metal or a metal salt as a precursor has been known (for example, refer to Non-Patent Document 1, 2, or 3) For example, when a metal alkoxide is used as a precursor, there may be a problem that the property may deteriorate due to remaining carbon, as well as a problem that a high temperature treatment is needed, or, when a chloride is used as a precursor, there may be a problem that halogen is evacuated. These precursors also have a problem that the precursors may be hydrolyzed by the water contained in the atmosphere, and, further, these precursors need a big amount of organic solvents, which is not preferred in view of the circumstance problem. Moreover, there have been problems that the thin film transistor (TFT) produced by using these metal oxide semiconductors exhibits a lower mobility, a smaller on/off ratio and a larger threshold value.
On the other hand, examples of manufacturing a thin film transistor by forming a metal oxide semiconductor film via a sputtering method are disclosed in Patent Documents 3 and 4. There may be a problem in the method using a vacuum apparatus such as sputtering that the manufacturing efficiency is not high, because a batch production is needed in such a method. Also, there has been a problem that the metal oxide semiconductor manufactured by using a sputtering method tends to have a property variation, and that a high temperature treatment after the production is needed to stabilize the property.    Patent Document 1: Japanese Patent Application Publication Open to Public Inspection (hereafter referred to as JP-A) No. 2003-179242    Patent Document 2: JP-A No. 2005-223231    Patent Document 3: JP-A No. 2006-165527    Non-Patent Document 1: “Kagaku-Kogyo”, 2006, December, “Synthesis of Oxide-Semiconductor Thin Film by Sol-Gel Method, and Its Application”    Non-Patent Document 2: Electrochemical and Solid-State Letters, 10(5) H135-H138    Non-Patent Document 3: Advanced Materials 2007, 19, 183-187    Non-Patent Document 4: IDW′ 07 (International Display Workshop 2007) p1783